Microelectromechanical systems (MEMS) microphones are widely used in voice communications, hearing-aid devices, and noise and vibration control applications. Various micromachining technology has been used to design and fabricate various MEMS microphones. Due to its high sensitivity, high signal-to-noise ratio (SNR), and long-term stability performance, the capacitive microphone is a very desirable and widely used type of microphone.
One significant limiting factor to the sensitivity of a MEMS microphone, however, is parasitic capacitance between the backplate and diaphragm of the microphone. Much of the research and development on solving this problem has focused on software calibration methods, including noise-reduction algorithms, and second-order directional microphones. Undesirably, those approaches require significant complexity and power. Accordingly, these solutions often increase overall cost of the ultimate device. When used in applications with limited power supplies (e.g., in hearing instruments, which often have very small batteries), these solutions reduce battery lifetime.